Rotatable lamps are typically supported by cantilevered spokes or support arms, often by a pair of opposed cantilevered arms. Proximal ends of the cantilevered arms are connected to a tenon fitter, while the distal ends are connected to casings provided on diametrically opposite sides of the housing of the lighting fixture. The casings permit pivotal movement of the housing between the arms, without damaging fixture wiring that passes internally through the arms. This type of mounting structure is described in U.S. patent application Ser. No. 07/725,485, filed Jul. 3, 1991 by Edgell et al., now U.S. Pat. No. 5,183,331, entitled CANTILEVERED SPOKE MOUNTING FOR LIGHTING FIXTURE, the subject matter of which is incorporated herein by reference.
The tenon fitted is typically a sleeve, to which the proximal ends of the cantilevered arms are connected. A tenon extends axially from the proximal end of the sleeve and is received in an open end of a mounting pole. Typically, the mounting pole has an outer diameter or dimension the same as that of the sleeve. The inner diameter of the mounting pole is slightly larger than the outer diameter of the tenon, which tenon is received in the open end of the mounting pole. When assembled, the axial end face of the mounting pole abuts the proximal end face of the sleeve.
Set screws have been used to secure the sleeve to the mounting pole. Tapped bores are provided circumferentially around the mounting pole near the upper end thereof. A set screw threadedly engages corresponding tapped bores such that end faces of the set screws extend inwardly to engage the outer surface of the tenon. The frictional engagement of the set screw end faces interlocks the tenon fitter with the mounting pole.
While set screws are for the most part adequate for securing the tenon fitter to the mounting pole, they tend to detract from the architecturally pleasing external appearance of the mounting system associated with the lighting fixture and to deteriorate from exposure to the environment. Moreover, a set screw applies a securing force at a specific point and thus may not provide a sufficient hold. Also, a single set screw may cause the tenon fitter and mounting pole to become eccentric so that the outer surfaces of the tenon fitter sleeve and mounting pole are misaligned. This misalignment will detract from the appearance of the structure. If more than one set screw is required to ensure proper alignment, the process of securing the tenon fitter becomes more time consuming and the problem of degrading the external appearance of the structure is exacerbated.
Examples of other types of housing mounting systems are disclosed in U.S. Pat. Nos. 1,389,013 to Schwartz; 3,246,135 to Husby; 3,519,811 to Jacobs; 1,283,480 to Duffy; and 4,722,502 to Mueller et al.